When a mobile phone is used in a bright ambient light environment, the reflection of the ambient light from the display can be very disruptive, making the content of the display difficult to read. Reflection of ambient light can occur at a number of surfaces, especially at the dense-rare boundaries of an optical component. As shown in FIG. 1, reflection can occur at a number of surfaces of the display and the window on top of the display. Incoming light beam L1 can reflect at the top and the bottom dense-air boundaries of the window. The reflected light from the first reflection at the top dense-rare boundary is denoted by R1. The reflected light from the second reflection at the bottom dense-rare boundary is denoted by R2. Similarly, light can also reflect from the top dense-rare boundary of the display, resulting in reflected light R3. It is advantageous and desirable to reduce or substantially eliminate the reflections.
Antireflection coatings are known in the art. Usually one or two thin films of coating material are coated on a substrate surface in a vacuum chamber to reduce the reflection by destructive interference. Antireflection coatings are generally expensive because of the cost involved in the vacuum evaporation process and the low yield of the coating. It is advantageous and desirable to provide a method of producing an antireflection surface that is cost-effective.
Sub-wavelength periodic structures have been used for antireflection purposes. A typical antireflection grating is shown in FIG. 2. As shown in FIG. 2, a surface structure 2 having a pitch P can be imparted on a substrate 5. To be used as an antireflection structure, the pitch P of the surface structure 2 must be smaller than the wavelength of the ambient light. Ophey et al. (U.S. Pat. No. 5,694,247, hereafter referred to as Ophey) discloses that a grating is imparted on optical components such as lenses and beam-splitters. In particular, Ophey discloses that in an optical transmissive device having an entrance surface and an exit surface for light transmission, the antireflection grating imparted on one surface is perpendicular to the antireflection grating imparted on another surface to avoid birefringent. Ophey discloses a molding technique combined with UV curing that is used to impart the grating on synthetic material layers comprised of poly-methyl methacrylate (PMMA) or polycarbonate (PC). Gaylord et al. (U.S. Pat. No. 5,007,708, hereafter referred to as Gaylord) discloses a number of techniques for producing antireflection grating surfaces on dielectrics, semiconductors and metals. In particular, Gaylord discloses surface-relief grating being formed by reactive ion etching, electron beam lithography, or holography.
While the prior art techniques have many advantages for their intended applications, they may not be applicable or cost-effective when the antireflection structure is used on a display that requires one or more polarization components.